The present invention relates to the field of antennas, and more particularly, to a phased array antenna employing an electromagnetic reflector and multiple transverse electromagnetic feeds each having a center conductor which generally transects the focal axis of the reflector.
A phased array antenna generally consists of a group of radio frequency energy radiating elements placed in close proximity to each other so that they provide the collective capability to steer an RF beam. The elements may range in size from miniature dipoles to huge parabolic dishes used in radio telescopes, depending on the desired operational characteristics of the antenna. The elements typically are arranged in a regular pattern with a spacing of one-half the wavelength of the RF energy to be received or transmitted by the antenna. If the elements are very close together, they will degrade each other's performance unless special precautions are taken. If they are far apart compared to the wavelength of interest, they cease acting collectively. The amplitude and phase of the input power to each element preferably are established to optimize the beam width, angle of maximum scan, side lobe level, and location of nulls in the radiation pattern of the antenna. The use of a phased array antenna permits the achievement of desirable applications such as the steering of the beam with simple elements with little intrinsic capability.
During the past several years there has been growing interest in developing wide band phased array antennas having a bandwidth of a decade or more. Conventional wide band phased array antenna systems use several antennas, where each antenna contributes a portion of the total operating bandwidth. However, the use of multiple antennas requires significant space, which is a limited resource on board ships or on the tops of buildings, where many antennas are located. Therefore, a need exists for a wide band phased array antenna system which overcomes the aforementioned limitations.
U.S. Pat. No. 3,881,178, "ANTENNA SYSTEM FOR RADIATING MULTIPLE PLANAR BEAMS," describes an antenna system for simultaneously radiating a plurality of planar beams into a region of space. The system includes a cylindrical radio frequency (RF) reflector having a focal axis, and includes feed horns which are oriented perpendicular to the focal axis of the reflector. However, this type of antenna uses feed horns which generate RF signals at a relatively narrow bandwidth. The beam from this antenna can only be steered in perpendicular direction with respect to the focal axis of the reflector in an elevation plane.